Hydrocarbon liquefaction processes are known in the art. Often, hydrocarbon liquefaction plants are designed to liquefy a specific hydrocarbon or mixture of hydrocarbons at specific feed conditions, for example natural gas or ethane at certain feed temperature, pressure, and composition.
It may be desirable to operate a liquefaction plant using different a feed stream than originally planned. For example, it may be desirable to liquefy ethylene at a plant originally designed to liquefy ethane. There exists therefore, a need for hydrocarbon liquefaction plants that are capable of efficiently liquefying a variety of feed streams.
It is also desirable to provide such flexibility, while also enabling the simultaneous liquefaction of multiple feed streams, each having a different composition, temperature, and/or pressure (hereinafter “different feed properties”). Regardless of the nature of the feed streams, it is also desirable to liquefy the feed streams in a manner that enables each product to be stored in a low-pressure tank (typically less than 2 bara and preferably less than 1.5 bara) and with little or no product flash (preferably less than 10 mole % vapor).
One option for liquefying multiple feed streams, each having different feed properties, and storing each product in a low pressure product tanks with minimum or no flash, would be to require the product streams to leave the main cryogenic heat exchanger (MCHE) at different temperatures. This option is undesirable because it would add complexity to the MCHE, including the addition of side-headers. Another option would be to have the product streams leave MCHE at the same temperature and sub-cool the least-volatile product stream beyond what is required for the storage. This option would require additional power or may lead to collapse of the product tank. In addition, the most volatile product may flash, leading to product loss or the need for re-liquefaction.
Accordingly, there is a need for a hydrocarbon liquefaction plant and process that is capable of liquefying multiple different feed streams with minimal product flash, that is capable of adjusting to changes in the properties of the feed streams, and is simple, reliable, and relatively inexpensive to construct, maintain, and operate.